This invention relates to a rotating, linearly propelled scanning antenna apparatus and method using radar, sonar, or the like, for use in locating buried objects.
In many applications it is important to be able to quickly and accurately locate objects such as pipes, cables, mines, and barrels that are buried beneath the surface of the earth. Such objects may be located using Ground Penetrating Radar (xe2x80x9cGPRxe2x80x9d) techniques in which electromagnetic waves are transmitted into the ground and reflected. (The term xe2x80x98groundxe2x80x99 includes soil, concrete, asphalt, and the like.) The reflections are analyzed according to methods that are well known in the art to determine the location of any object that may be buried there beneath. Other methods well known in the art may also be used, including sonar techniques and inductive techniques.
GPR techniques use transmitting antennas to emit the electromagnetic waves that propagate into the ground and interact with the buried objects. This interaction results in a scattered wave, which is measured by the receiving antenna of the GPR device. By changing the location of the transmitting antenna and recording the corresponding signal that is received and then output by the receiving antenna as a function of time (or frequency) and location, one obtains the radar data from which the information about the buried objects may be extracted. However, for the radar data to be useful, the positions of the measurement locations must be accurately known. Further, it is important for cost efficiency that the system be able to cover a large area in a short period of time; that is, it is important that the system have a high survey speed, which means that the antenna must travel at a high speed.
Such high speed movement may create undesirable mechanical stresses on the antennas. For example, in the simplest scanning system the antenna moves linearly back and forth across the width of the scanning area. This back and forth linear motion requires that the antenna slow down, stop, and then speed up each time it reaches the edge of the scanning area. This type of back and forth movement creates tremendous mechanical stresses in the antennas and survey system when the system is operated at a high survey speed. In fact, these extreme stresses severely limit the survey speed that is obtainable with a linear scanning system.
It is an object of the current invention to provide a rotating GPR system for which the antenna speed and survey speed can be very high without causing excessive mechanical stresses on the antennas and scanning system. With a rotating system, the antennas do not have to slow down when they reach the edge of the scanning area, but instead may operate at a constant speed. As a consequence, the mechanical stresses are much less for a rotating GPR system than for a linear GPR system.
A rotating GPR system is described in U.S. Pat. No. 4,967,199 (xe2x80x9cGround Probing Radar Method and Apparatusxe2x80x9d) to Gunton et al. and in Surface Penetrating Radar by D. J. Daniels (IEE Press, 1996, pp. 200-204). Those references describe a system in which the antennas are interleaved spirals whose axes correspond with the axis of rotation. Further, unlike the present invention, the rotation in these systems is used solely to reduce clutter rather than to move the antenna system along the ground.
According to the objects of the present invention, a ground penetrating antenna apparatus is described providing an antenna housing, one or more supporting extensions that are rotatably affixed to the antenna housing about a first axis, at least one antenna that has transmit and receive elements and that is rotatably affixed to a supporting extension about a second axis that is different from the first axis, a linear propulsion mechanism that is attached to the housing so that the housing may be moved over the ground, an impulse generator that is electrically coupled to each transmit element so as to provide pulses to each transmit element, and a sampling unit that is electrically coupled to each receive element so as to receive the output from each receive element.
In one embodiment of the present invention, the ground penetrating antenna apparatus comprises radar antennas. In a father embodiment, a supporting extension is responsive to the linear propulsion mechanism. In yet another embodiment, a supporting extension is coupled to the linear propulsion mechanism via a transmission mechanism.
In one embodiment of the present invention, each supporting extension rotates at a constant rate of rotation. In another embodiment, each supporting extension rotates at a constant rate and the antenna rotates at a constant rate of rotation that is equal in magnitude and opposite in direction to the constant rate of rotation of each supporting extension.
In one embodiment of the present invention, the linear propulsion mechanism comprises a cart that is coupled to the housing and a means for propelling the cart. In another embodiment, the linear propulsion mechanism comprises a self-propelled vehicle that is coupled to the housing.
In one embodiment of the present invention, the ground penetrating antenna apparatus further comprises a data storage device for storing the radar data collected from the sampling unit. In another embodiment, the apparatus further comprises a position indicator that is coupled to the supporting extension and the linear propulsion mechanism. In yet another embodiment, the apparatus further comprises a data storage device for storing the radar data collected from the sampling unit and the position data collected from the position indicator. In another embodiment, each element of the radar data corresponds to a unique element of the position data.
Also in accordance with the objects of the present invention, a method is provided for locating underground objects within a surface area consisting of providing a housing that is adapted for linear movement, providing a supporting extension that is rotationally coupled to the housing about an axis, providing an antenna that is rotationally coupled to a supporting extension about an axis different from said axis of said supporting extension, providing electronics coupled to the antenna that is capable of receiving ground penetrating antenna data, rotating a supporting extension about the axis of the supporting extension, rotating the antenna about the axis of the antenna, moving the housing along a path within the surface area, receiving ground penetrating antenna data at selected positions along the path, recording the ground penetrating antenna data and the selected positions, and analyzing the recorded antenna data and the recorded selected positions to locate underground objects. In one embodiment, the antenna is a radar antenna.
In one embodiment of the present invention, the step of rotating a supporting extension further comprises rotating a supporting extension at a constant rate of rotation. In another embodiment, the rotating step comprises rotating an antenna at a constant rate that is equal in magnitude and opposite in direction to the constant rate of rotation of a supporting extension.
In one embodiment of the present invention, the step of moving the housing further comprises moving the housing responsively to rotating a supporting extension. In another embodiment, the step of moving the housing further comprises providing a cart that is coupled to the housing and propelling the cart. In yet another embodiment, the step of moving the housing further comprises providing a self-propelled cart that is couples to the housing. In another embodiment, the recorded antenna data is converted from polar coordinates to rectangular coordinates.